The UK Departments of Health now recommend annual influenza vaccination for all children 2-7 years of age, with children over 7 years eligible for vaccination if in certain higher risk clinical categories. Though data are available documenting the safety and immunogenicity of LAIV in this age group, there are little data to assess efficacy and immune correlates in UK children, and in particular atopic children. This study will enrol 200 children (and at least 200 unvaccinated household sibling controls), many with a history of asthma or recurrent wheezing, and allow an assessment of efficacy, safety and immune correlates in these children, and how this varies with prior administration of pandemic influenza vaccine and/or LAIV.

Inclusion Criteria:

• Aged 2 - 18 years old
• Written informed consent from parent/guardian (or patient themselves from age 16 years), with assent from children aged 8 years and above wherever possible.

Exclusion Criteria:

• Hypersensitivity to the active ingredients, gelatin or gentamicin (a possible trace residue) [notwithstanding allergy to egg protein]

• Previous systemic allergic reaction to LAIV

• Previous allergic reaction to an influenza vaccine (not LAIV) is a relative contra-indication, which must be discussed with the site PI to confirm patient suitability

• Children/adolescents who are clinically immunodeficient due to conditions or immunosuppressive therapy such as: acute and chronic leukaemias; lymphoma; symptomatic HIV infection; cellular immune deficiencies; and high-dose corticosteroids**.

  **High-dose steroids is defined as a treatment course for at least one month, equivalent to a dose of prednisolone at 20mg or more per day (any age); or for children under 20kg, a dose of 1mg/kg/day or more.

• Children and adolescents younger than 18 years of age receiving salicylate therapy because of the association of Reye's syndrome with salicylates and wild-type influenza infection.

• pregnancy

• Febrile ≥ 38.0 'C in last 72 hours

• Acute wheeze in last 72 hours requiring treatment beyond that normally prescribed for regular use by the child's treating healthcare professional

• Recent admission to hospital in last 2 weeks for acute asthma

• Current oral steroid for asthma exacerbation or course completed within last 2 weeks

• Received any blood or blood products within the past 12 weeks

• Any other significant condition or circumstance which, in the opinion of the investigator, may either put the participant at risk because of participation in the study, or may influence the result of the study, or the participant's ability to participate in the study.